Ophthalmoscopic camera

ABSTRACT

An ophthalmoscopic camera is provided which can eliminate undesired light reflected from the cornea of an eye to be examined and the front and back surfaces of a front objective through which the illumination light passes by interposing a ring-shaped aperture between a plane reflecting mirror and a condenser lens arranged next to the reflecting mirror and a small shield between said condenser lens and the next condenser lens so as to shield a small area in the vicinity of and including the optical axis. The optical system for photography includes no such shield as described above and said photographic objective is of biconvex, thereby increasing the picture angle to 45*.

United States Patent [72] Inventor Hiroltuu Olmjima TokyoJlpan |2l|App]. No. 864,327 [22] Filed Oct. 7, 1969 [4S] Patented July 20, I971[73] Assignee NipponKogakn ILK.

TokyoJlpnn [54] OPHTHALMOSCOPIC CAMERA 2 Claims, 4 Drawing Figs.

[52] U.S.Cl 351/7, 95Ill [5|] A6lb3/l4, G03b l9l02, A6lb 3Il 0 [50]351/7; 95lllE,llM,llBS

[$6] Reierenees Cited UNITED STATES PATENTS 3,089,398 5/1963 Wilms 35l/7X 3,259,04! 7/l966 Okajima Primary Examiner-David Schoenberg AssistantExaminer-Paul A Sacher Attorney-Ward, McElhannon, Brooks & FitzpatrickABSTRACT: An ophthalmoscopic camera is provided which can eliminateundesired light reflected from the cornea of an eye to be examined andthe front and back surfaces of a from objective through which theillumination light passes by interposing a ring-shaped aperture betweena plane reflecting mirror and a condenser lens arranged next to thereflecting mirror and a small shield between said condenser lens and thenext condenser lens so as to shield a small area in the vicinity of andincluding the optical axis. The optical system for photography includesno such shield as described above and said photographic objective is ofbiconvex, thereby increasing the picture angle to 45.

PATENIEU JUL20I97| 3594-071 sum 1 er 2 FIG. I [P'] I [all] [H] 3 VEi:r-8

cit -6 sum 2 or 2 FIG. 3

OPIITI'IALMOSCOPIC CAMERA The present invention relates to anophthalmoscopic camera.

In case of the opthalmoscopic camera of the type in which one portion ofthe optical system for photography is used in common as one portion ofthe illumination optical system, the illumination light is reflected bythe cornea of an eye to be examined or by other optical components anddirected into the optical system for photography, thereby causingflares, ghosts, etc. so that no clear, sharp image of the retina can beobtained.

In order to eliminate such undesired reflected light, there has beenproposed a method in which instead of a plane reflecting mirror, aconcave reflecting mirror is disposed at an angle relative to theoptical axis of the photographic optical system at a point where thelight from the illumination optical system enters into the optical axisof the photographic optical system, and another method in which ameniscustype lens is used as a photo-objective through which theillumination light passes and a small shield is provided in the vicinityof the optical axis of the meniscus lens including the optical axis. Inthe former method, the aberration is increased because of the inclinedconcave reflecting mirror so that this method is not suitable forphotography of the fundus of an eye to be examined with a high degree ofaccuracy. In the latter method, the shield must be provided along theoptical axis of the photographic optical system so that in some cases, afocused image flight flux corresponding to one point of the retina willbe interrupted by this shield when the light flux is too fine as in thecase of the ophthalmoscopic camera. Furthermore, it is difiicult toincrease the picture angle above 30 because of the meniscus lens.

The present invention has for its primary object to eliminate thesedefects as described above of the conventional ophthalmoscopic camera.

The present invention provides an ophthalmoscopic camera in which abiconvex lens is used as an objective lens of the character describedabove thereby to increase the angle of view to approximately 45 and theundesired reflected light as described above will be effectivelyeliminated without providing a shield of the type described above alongthe optical axis of the photographic optical system.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofone embodiment thereof with reference to the accompanying drawing, inwhich:

FIG. I is a diagrammatic view illustrating an optical system of aconventional opthalmoscopic camera provided with means for preventingundesired reflected light; and

FIGS. 2, 3, and 4 are diagrammatic views illustrating one embodiment ofthe present invention, FIG. 2 illustrating the optical system, FIG. 3being for explanation of the function of the optical system and FIG. 4being for further explanation of a portion of FIG. 3.

FIG. I shows the conventional system above described in which a meniscustype lens 3 is used as a photo-objective through which the illuminationlight emanated from a light source 6 and passing lenses 7, 8 and 9passes for illuminating the cornea 2 and fundus l to be examined.

FIGS. 2 through 4 show an illustrative embodiment of the presentinvention.

Referring to FIG. 2, light emanated from a light source 6 and passingthrough a first condenser lens 7, a second condenser lens 8 and a thirdcondenser lens 9 is reflected by a planar reflecting mirror M which hasa centered aperture [M] and is disposed at an angle relative to theoptical axis, and is directed along the axis of photographic opticalsystem toward an eye to be examined reaching the fundus 1 through afirst objective lens 3 and the cornea 2. (The above is the descriptionof the illumination light.) After illuminating the fundus I, the lightis reflected as "photographic light" which reaches a film through thecornea 2, the first objective lens 3, the

center aperture [M] of the planar reflecting mirror M, the aperture [H]of a stop H and a second objective lens 4, thereby focusing the image ofthe retina. (The above is the description of the light for photography.)

In the optical path of the illumination light, there are three places atwhich the undesired reflected light is produced, that is, the cornea 2,and the front and back surfaces a and b of the first objective lens 3.In order to prevent the undesired light reflected from the cornea 2, thewell-known ring illumination method is employed.

First the method of the ring illumination will be described. Aring-shaped aperture (P,] is provided at a position P (See FIGS. I and2) of the illumination optical system in real conjugated relation withthe cornea 2. Therefore, the illumination light passing through thecornea 2 may be limited to a ring portion lP,'] (See FIG. 3) which isgeometrically conjugated with the ring lPI], so that reflected lightoccurs only at the ring portion [P,']. In order to prevent thisreflected light, a sufficiently large circular aperture [H] is providedat the position H in the photographic optical system and in realconjugated relation with the cornea 2 to thereby interrupt the realimage of the ring portion [P,], so that the light flux which passesfreely through the circular aperture [H] is ensured not to include anylight reflected from the cornea 2.

Next the method of the present invention for preventing the light frombeing reflected upon the front and back surfaces 0 and b of the firstobjective lens 3 will be described. Upon the upper surface P, of thesecond condenser lens 8 is desposed a small black dot [P,] in order toshield a small the lens 8 about the optical axis of the lens 8 (FIG. 2).The conjugated relation of this small black point upon which is basedthe present invention will be described in order to explain theinterrelation among the optical parts or components described aboveincluding the black point.

When an arbitrary object positioned at the point P, is focused by theillumination light and its partially reflected light, the conjugatedrelation is determined in the following manner. That is, the light whichis emanated from the point P, and passes through the third condenserlens 9 and the planar reflecting mirror M is once focused in thevicinity of the vertex of the back surface b of the first objective lens3, thereby forming an intermediate image P. A portion of the light isreflected by the surface b and directed toward the aperture stop H (Thisreflected light will be referred to as b-reflected light" hereinafter).The remaining light not reflected upon the surface b is refracted at thesurface b and reaches the surface a, where a portion of the lightthereof is reflected and then refracted at the b-surface, thus reachingthe aperture stop H and forming the real image of P,. (This will bereferred to as "rt-reflected light" hereinafter.) The reflected lightwhich adversely affects the ophthalmosopic photography is of course"aand b-reflected light. (See dotted lines in FIG. 3.)

When the bsurface is convex, among theb-reflected reflected light, thelight flux which can freely pass through the aperture H is that which isreflected from the limited area in the vicinity of the vertexof'theb-surface so that the black point [P is provided at the point P,thereby preventing the reflection, thereby attaining indirectly theshielding performance.

Let 22 be the diameter of the intermediate image [Pf] of [P upontheb-surface required for the indirect shielding, then Z may be obtainedby the following relation by the law of reflection:

(x/Lir 'y/ p) where R=the radius of curvature of the vertex of theb-surface;

2x=diameter of the aperture H;

2y=the maximum diameter of the ring-shaped aperture stop l il;

Lu and L =distances from the center of curvature C of the b-surface to Hand P respectively, and in practice, L,,=

L,,, but for the sake of clear explanation different characters areused. (See FIG. 4.)

As to the a-reflected light, it will be understood that the conjugatedreal image of the black point [P,] is superposed upon the aperture stopH because of the above-described conjugated relation. Therefore, thisimage must be sufficient enough to shield the aperture [H] of theaperture stop H.

In this embodiment the black point {P and the ring-shaped aperture stop[PJ have been described as being formed upon the upper surfaces of thesecond and third condenser lenses 8 and 9 respectively, but theirpositions may be displaced if desired based upon the principle of thepresent invention described herein.

From the foregoing, it will be understood that the present invention canform a very clear, sharp image of the fundus of an eye to be examinedbecause undersired light (which adversely affects the photography)reflected by the cornea and the curved surface of the first objectivelens can be completely eliminated.

What I claim is:

I. A device for the photography of a fundus, particularly a retina of aneye, comprising, a main optical viewing system including a b t-convexphotographic objective placed on an optical axis of the eye for formingan intermediate image of the retina, and an aperture stop placed at aposition conjugate with the cornea of the eye with respect to thephotographic objective; an illuminating system comprising a light sourceand an illuminating optical arrangement for projecting an image of saidlight source on the cornea of the eye sequentially including saidphotographic objective, and apertured inclined mirror placed betweensaid photographic objective and said aperture stop for reflecting theilluminating light rays toward the optical axis of said objective and anoptical system, whereby the optical axis of said optical system isarranged transversely to the axis of said photographic objective, saidmirror is centrally positioned with respect to both the viewing systemand optical system axes; said optical system further including firstcondenser lens proximate said light source followed by first and secondpositive lens means, a ring-shaped aperture having a central obscuringportion, said ring-shaped aperture being provided on a surface of saidsecond positive lens means and positioned with respect to saidphotographic objective and said photographic objective and said inclinedmirror to produce an intermediate image of said ring aperture insubstantial coincidence with said cornea, a center obscuring spotdiaphragm placed on the optical axis of said optical system between saidlight source and said ring aperture, said spot diaphragm being providedon a surface of said first positive lens means with the lens elements ofsaid illuminating optical arrangement so positioned as to form anintermediate image of said spot diaphragm on the rear surface of saidphotographic objective, whereby the curvature of the objective acts as aconvex mirror for further forming said inter mediate image of said spotdiaphragm on said aperture stop.

2. A device according to claim I, wherein said first positive lens meansis a planoconvex lens, said spot diaphragm being provided on the planesurface of said first positive lens means, said and said ring aperturebeing provided on the plane surface of said second positive lens means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,594,071 Dated July 20th, 1971 lnventm-(s) Hirokazu Okajima It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

(COUNTING FROM LINE 1 IN THE RESPECTIVE COLUMN AND WITHOUT REFERENCE TOTHE LINE NUMBERS APPEARING BETWEEN THE COLUMNS WHICH ARE OUT OF PHASEWITH THE LINES) Column 2, line 29, change "the lens 8" to portion line53, change "theb" to the b line 56, change "theb" to the b line 61,change "theb" to the b Column 4, line 28, after "said", insert secondpositive lens means is a lano-convex lens Signed and sealed this 18thday of April 1972.

(SEAL) Attest:

EDWARD M.FLETCH:ER, JR. ERT TTSCHALK Attes'ting Officer CommissionerofPatents DRM PC1-1050 "069) uscoMM-Dc scam-P00 U 5 GOVERNMENT PR\NT|NGQFFlCE 19, 0-356!!!

1. A device for the photography of a fundus, particularly a retina of aneye, comprising, a main optical viewing system including a bi-convexphotographic objective placed on an optical axis of the eye for formingan intermediate image of the retina, and an aperture stop placed at aposition conjugate with the cornea of the eye with respect to thephotographic objective; an illuminating system comprising a light sourceand an illuminating optical arrangement for projecting an image of saidlight source on the cornea of the eye sequentially including saidphotographic objective, and apertured inclined mirror placed betweensaid photographic objective and said aperture stop for reflecting theilluminating light rays toward the optical axis of said objective and anoptical system, whereby the optical axis of said optical system isarranged transversely to the axis of said photographic objective, saidmirror is centrally positioned with respect to both the viewing systemand optical system axes; said optical system further including firstcondenser lens proximate said light source followed by first and secondpositive lens means, a ring-shaped aperture having a central obscuringportion, said Ring-shaped aperture being provided on a surface of saidsecond positive lens means and positioned with respect to saidphotographic objective and said photographic objective and said inclinedmirror to produce an intermediate image of said ring aperture insubstantial coincidence with said cornea, a center obscuring spotdiaphragm placed on the optical axis of said optical system between saidlight source and said ring aperture, said spot diaphragm being providedon a surface of said first positive lens means with the lens elements ofsaid illuminating optical arrangement so positioned as to form anintermediate image of said spot diaphragm on the rear surface of saidphotographic objective, whereby the curvature of the objective acts as aconvex mirror for further forming said intermediate image of said spotdiaphragm on said aperture stop.
 2. A device according to claim 1,wherein said first positive lens means is a planoconvex lens, said spotdiaphragm being provided on the plane surface of said first positivelens means, said and said ring aperture being provided on the planesurface of said second positive lens means.